A number of different types of devices have been used in the past for the spreading of streams of dry solids from a relatively narrow to a relatively wide stream.
Sloped flat plates down which the stream flows, and spreads as it flows, have been used. But such a device provides only limited spreading and has the further disadvantage of causing particle segregation because the larger particles migrate to the edges of the stream as the stream spreads.
Sloped plates having baffles attached thereto for mechanically deflecting portions of the stream have been used but these produce erratic spreading patterns under variable conditions, i.e., of flow rate, moisture content of the dry particles, etc.
Vibrating or shaking feeders have been used but these are unduly complicated and costly due to the necessity for incorporation of an additional piece of machinery (powered machinery) in the system. Further, they have substantially the same performance limitations as the sloped plate device referred to above.
Surge bins with feeders (generally vibrating feeders) have been used but these also are costly, require excessive headroom, and necessitate the provision of controls which interrupt or vary stream flow to prevent overfilling of the bin.
Chutes having metal plates which form fixed conical surfaces provide improved results when operated under full head as with a surge bin and feeder (referred to above) but they still, when so operated, have the limitations of the surge bin device. When operated under free flow conditions metal conical chutes of fixed cross-section are erratic when changes in conditions are encountered, such as variations in the velocity or flow rate of the solid stream, or variations in the physical characteristics of the dry solids which form the flowing stream. Further, they do not perform well when supplied with an off center feed.
Power operated screws, agitators and other spreaders are costly and do not accommodate easily to variations in the dry solid stream (particularly oversized lumps), as referred to above.